The nondispersive infrared (NDIR) technique is widely used for the detection of gas leaks. Such gas analyzers utilize the principle that various gases absorb infrared radiation at characteristic wavelengths. Typically, a narrow band infrared transmission filter is used to isolate the infrared band of interest in NDIR gas analyzers. The NDIR technique advantages include gas detection specificity, measurement stability, and high speed of response. Remote monitoring of gaseous products with no external source of infrared radiation may be realized using specific measurements of infrared radiation and rationalizing the signals from gas-reference cell pairs. Sensitivity of these methods is considerably lower than that of the methods that include infrared laser illuminating and "pumping" up gas plume radiation. Also a presence of moving mechanical parts decreases a reliability and precision of this systems. Another technique of gas leak location comprises directing a beam of coherent high intensity infrared radiation into potential plume direction, and the wave length of the beam is selected such that it energized selected molecules. The imager receives both backscattered laser light and background radiation. When a detectable gas is present, the backscattered laser light is highly attenuated, producing a region of contrast or shadow on the image. This techniques uses an infrared video camera and other technical means, which require a separate source of cooling, which increases the cost of device and maintenance, and reduces the portability of the system. The technique does not eliminate background effects from the signal. These methods and apparatus do not provide a quantitative information about gas concentration in the cloud surrounding leak area. An effectiveness of these methods highly depends on the background properties. Gas visualization apparatus cannot clearly distinguish between the infrared gas absorption information of gas leakage and the background information, are not portable and do not provide a quantitative information of gas concentration. From the other hand, methods using gasfilter correlation technique usually are passive methods with lower sensitivity and precision in case of small leaks at the distance.
It is therefore desirable to provide portable and sensitive means to detect gas leaks at the distance, which will not depend on background properties.